Your brain is built of cells called neurons and glia—hundreds of billions of them. Each one of these cells is as complicated as a city. And each one contains the entire human genome and traffics billions of molecules in intricate economies. Each cell sends electrical pulses to other cells, up to hundred of times per second. If you represented each of these trillions and trillions of pulses in your brain by a single photon of light, the combined output would be blinding.

The cells are connected to one another in a network of such staggering complexity that it bankrupts human language and necessities new strains of mathematics. A typical neuron makes about ten thousand connections to neighboring neurons. Given the billions of neurons, this means there are as many connections in a single cubic centimeter of brain tissue as there are stars in the Milky Way Galaxy.

Below are several other interesting and surprising facts about our brains from Eagleman’s Incognito.

1. We’re notoriously poor observers of our environment.

But we have the false idea that we see things just as they are. Still, we can very easily miss stimuli that are right in front of our eyes if we’re not looking for them. Similarly, we don’t see just with our eyes. We see with our brains. The phenomenon of “change blindness” illustrates these points perfectly.

Consider the following experiment: Random people passing through a courtyard are asked for directions by an experimenter. During the conversation, workers carrying a door walk in between the person and experimenter. After the interruption, most of the people simply continue giving directions, picking up where they left off—even though they’re talking to a completely different person! That’s because another person involved with the experiment (known as a confederate) hid behind the door and switched places with the original experimenter.

Eagleman writes: “In other words, they [the participants] were only encoding small amounts of the information hitting their eyes. The rest was assumption.”

Another good example is magic tricks. Magicians’ “actions should give away the game—but they can rest assured that your brain processes only small bits of the visual scene, not everything that hits your retinas.”

To learn more about change blindness, check out this website, which is maintained by a psychologist, and this cool video.

2. Some people experience the world differently than most of us — and it’s totally normal.

Here, we’re not talking about debilitating disorders like schizophrenia, when a person’s brain produces visual, tactile or auditory hallucinations (or delusions). Rather, for some people, there are “magenta Tuesdays, tastes that have shapes and wavy green symphonies,” writes Eagleman. He says that one in 100 people experiences the world like this. And there’s a name for this not-so-uncommon condition: synesthesia.

Basically, people experience a mix of sensations simultaneously, and they do so automatically and regularly. They don’t just hear music; they might also taste it. Eagleman gave more examples in Incognito: “…the feel of sandpaper might evoke an F-sharp, the taste of chicken might be accompanied by a feeling of pinpoints on the fingertips, or a symphony might be experienced in blues and golds.”

One type of synesthesia is called “spatial sequence synesthesia.” These individuals have locations for time and any other numbers. For instance, “They can point to the spot where the number 32 is, where December floats or where the year 1966 lies.”

Surprising, right? What’s interesting is that these people are so used to experiencing the world this way that they’re surprised others don’t have this “joined sensation,” Eagleman explains. “The mere existence of synesthesia demonstrates that more than one kind of brain—and one kind of mind—is possible.”

We thrive on patterns and try to make sense of our world. We do the same thing when it comes to our own behaviors. According to Eagleman, “We have ways of retrospectively telling stories about our actions as though the actions were always our idea.”

Take the example of patients who’ve had split-brain surgery (when the corpus callosum is severed to help patients with epilepsy). In a 1978 experiment of patients who had this kind of surgery, researchers showed an image of a chicken claw to a patient’s left hemisphere and an image of a snow-filled winter scene to the right hemisphere. When asked to pick the image that symbolized what they’d seen, the patient’s right hand chose a card with a chicken, and their left hand chose one with a snow shovel. As Eagleman writes:

The experimenters asked him why he was pointing to the shovel. Recall that his left hemisphere (the one with the capacity for language) had information only about a chicken, and nothing else. But the left hemisphere, without missing a beat, fabricated a story: “Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.” When one part of the brain makes a choice, other parts can quickly invent a story to explain why.

This rationalization also occurs when patients are given a command. Eagleman continues:

If you show the command “Walk” to the right hemisphere (the one without language), the patient will get up and start walking. If you stop him and ask why he’s leaving, his left hemisphere, cooking up an answer, will say something like “I was going to get a drink of water.”

But this doesn’t happen just to split-brain patients, Eagleman says. We all do it. Participants instructed to hold a pencil in between their teeth while reading a passage found it funnier. That’s because their brains tried to account for the smiles. Sitting up straight also made others happier because the brain again assumed that this meant they were feeling good.

Other experiments have shown the same thing: that our brains love to spin a story. Eagleman recounts an experiment he and a colleague devised in the mid-1990s. Their goal was to test simple decision-making. Participants were asked to pick between two cards on a computer screen: A and B. There was no indication of which was the better choice, so participants picked the cards at random. But they did receive a small monetary reward after each one. In the next phase, the cards were reset and they had to pick between A and B yet again. But the rewards were now different. What the participants didn’t know was that the researchers created a formula to determine the reward, which was too difficult for the participants to detect. This formula factored in the participants’ card choices.

After the experiment, participants were asked why they picked the cards they did, and they gave a variety of explanations. According to Eagleman:

I was surprised to hear all types of baroque explanations, such as “The computer liked it when I switched back and forth” and “The computer was trying to punish me, so I switched my game plan.” In reality, the players’ descriptions of their own strategies did not match what they had actually done, which turned out to be highly predictable. Nor did their descriptions match the computer’s behavior, which was purely formulaic. Instead, their conscious minds, unable to assign the task to a well-oiled zombie system, desperately sought a narrative. The participants weren’t lying; they were giving the best explanation they could­—just like the split-brain patients…”

By the way, if you enjoy learning about the brain and brain disorders, check out neuropsychologist Paul Broks’s columns in Prospect magazine. According to the excellent blog Mind Hacks:

The ‘Out of Mind’ column ran for the best part of five years. Alternately whimsical, profound and poetic, it recounted ephemeral scenes from meetings with brain altered individuals and spun them into reflections on the science and philosophy of human nature.